1. Field of the Invention
This invention relates to compositions useful in the microelectronics industry for cleaning semiconductor wafer substrates. Particularly, this invention relates to alkaline stripping or cleaning compositions containing metal ion-free silicates that are used for cleaning wafers having metal lines and vias by removing metallic and organic contamination without damaging the integrated circuits.
2. Description of the Prior Art
An integral part of microelectronic fabrication is the use of photoresists to transfer an image from a mask or reticle to the desired circuit layer. After the desired image transfer has been achieved, an etching process is used to form the desired structures. The most common structures formed in this way are metal lines and vias.
The metal lines are used to form electrical connections between various parts of the integrated circuit that lie in the same fabrication layer. The vias are holes that are etched through dielectric layers and later filled with a conductive metal. These are used to make electrical connections between different vertical layers of the integrated circuit. A halogen containing gas is generally used in the processes used for forming metal lines and vias.
After the etching process has been completed, the bulk of the photoresist may be removed by either a chemical stripper solution or by an oxygen plasma ashing process. The problem is that these etching processes produce highly insoluble metal-containing residues that may not be removed by common chemical stripper solutions. Also, during an ashing process the metal-containing residues are oxidized and made even more difficult to remove, particularly in the case of aluminum-based integrated circuits. See, xe2x80x9cManaging Etch and Implant Residue,xe2x80x9d Semiconductor International, August 1997, pages 56-63.
An example of such an etching process is the patterning of metal lines on an integrated circuit. In this process, a photoresist coating is applied over a metal film then imaged through a mask or reticle to selectively expose a pattern in the photoresist coating. The coating is developed to remove either exposed or unexposed photoresist, depending on the tone of the photoresist used, and produce a photoresist on the metal pattern. The remaining photoresist is usually hard-baked at high temperature to remove solvents and optionally to cross-link the polymer matrix. The actual metal etching step is then performed. This etching step removes metal not covered by photoresist through the action of a gaseous plasma. Removal of such metal transfers the pattern from the photoresist layer to the metal layer. The remaining photoresist is then removed (xe2x80x9cstrippedxe2x80x9d) with an organic stripper solution or with an oxygen plasma ashing procedure. The ashing procedure is often followed by a rinsing step that uses a liquid organic stripper solution. However, the stripper solutions currently available, usually alkaline stripper solutions, leave insoluble metal oxides and other metal-containing residues on the integrated circuit.
Another example of such an etching process is the patterning of vias (interconnect holes) on an integrated circuit. In this process, a photoresist coating is applied over a dielectric film then imaged through a mask or reticle to selectively expose a pattern in the photoresist coating. The coating is developed to remove either exposed or unexposed photoresist, depending on the tone of the photoresist used, and produce a photoresist on the metal pattern. The remaining photoresist is usually hard-baked at high temperature to remove solvents and optionally to cross-link the polymer matrix. The actual dielectric etching step is then performed. This etching step removes dielectric not covered by photoresist through the action of a gaseous plasma. Removal of such dielectric transfers the pattern from the photoresist layer to the dielectric layer. The remaining photoresist is then removed (xe2x80x9cstrippedxe2x80x9d) with an organic stripper solution or with an oxygen plasma ashing procedure. Typically, the dielectric is etched to a point where the underlying metal layer is exposed. A titanium or titanium nitride anti-reflective or diffusion barrier layer is typically present at the metal/dielectric boundary. This boundary layer is usually etched through to expose the underlying metal. It has been found that the action of etching through the titanium or titanium nitride layer causes titanium to be incorporated into the etching residues formed inside of the via. Oxygen plasma ashing oxidizes these via residues making them more difficult to remove. A titanium residue removal enhancing agent must therefore be added to the stripper solution to enable the cleaning of these residues. See xe2x80x9cRemoval of Titanium Oxide Grown on Titanium Nitride and Reduction of Via Contact Resistance Using a Modern Plasma Asherxe2x80x9d, Mat. Res. Soc. Symp. Proc., Vol. 495, 1998, pages 345-352. The ashing procedure is often followed by a rinsing step that uses a liquid organic stripper solution. However, the stripper solutions currently available, usually alkaline stripper solutions, leave insoluble metal oxides and other metal-containing residues on the integrated circuit. There are some hydroxylamine-based strippers and post-ash residue removers on the market that have a high organic solvent content, but they are not as effective on other residues found in vias or on metal-lines. They also require a high temperature (typically 65xc2x0 C. or higher) in order to clean the residues from the vias and metal-lines.
The use of alkaline strippers on microcircuit containing metal films has not always produced quality circuits, particularly when used with metal films containing aluminum or various combinations or alloys of active metals such as aluminum or titanium with more electropositive metals such as copper or tungsten. Various types of metal corrosion, such as corrosion whiskers, pitting, notching of metal lines, have been observed due, at least in part, to reaction of the metals with alkaline strippers. Further it has been shown, by Lee et al., Proc. Interface ""89, pp. 137-149, that very little corrosive action takes place until the water rinsing step that is required to remove the organic stripper from the wafer. The corrosion is evidently a result of contacting the metals with the strongly alkaline aqueous solution that is present during rinsing. Aluminum metal is known to corrode rapidly under such conditions, Ambat et al., Corrosion Science, Vol. 33 (5), p. 684. 1992.
Prior methods used to avoid this corrosion problem employed intermediate rinses with non-alkaline organic solvents such as isopropyl alcohol. However, such methods are expensive and have unwanted safety, chemical hygiene, and environmental consequences.
The prior art discloses several organic strippers used to remove bulk photoresist after the etching process. U.S. Pat. Nos. 4,765,844, 5,102,777 and 5,308,745 disclose photoresist strippers comprising various combinations of organic solvents. These strippers, however, are not very effective on wafers that have been xe2x80x9cashedxe2x80x9d with oxygen plasmas as described above. Some photoresist strippers attempt to address this problem by adding additional water and an organic corrosion inhibitor such as catechol. Such compositions are disclosed in U.S. Pat. Nos. 5,482,566, 5,279,771, 5,381,807, 5,334,332, 5,709,756, 5,707,947, and 5,419,779 and in WO 9800244. In some cases, the hydrazine derivative, hydroxylamine, is added as well. Because of its toxicity, the use of catechol gives rise to various environmental, safety, and health concerns.
Metal silicates have been included as corrosion inhibitors in cleaning solutions used on electronic circuit boards. Examples of such solutions are disclosed in SU 761976, DD 143,920, DD 143,921, U.S. Pat. Nos. 5,264,046, 5,234,505, 5,234,506, and 5,393,448. The metal lines on circuit boards are much larger than those found in integrated circuits thus have less demanding cleaning requirements. In the case of integrated circuits, metal contamination introduced from a cleaning solution, even at extremely low concentrations, can cause premature failure of the device. Therefore, any formulation containing intentionally added metals, such as the metal silicates cited above, would be detrimental to integrated circuit device performance and reliability. U.S. Pat. No. 4,659,650 discloses using a sodium metasilicate solution to dissolve metal lift-off masks.
In U.S. Pat. No. 5,817,610 and EP 829,768 the use of a quaternary ammonium silicate, quaternary ammonium hydroxide and water is disclosed for use in removing plasma etch residues. In these two disclosures, catechol oligimers are preferred over quaternary ammonium silicates as corrosion inhibitors and no examples of quaternary ammonium silicates being used as corrosion inhibitors are shown. In U.S. Pat. No. 5,759,973 and EP 828,197 the use of a quaternary ammonium silicate, an amine compound, water and optionally an organic polar solvent is disclosed for use as a stripping and cleaning composition. None of the four disclosures cited above discloses the advantages of adding an aminocarboxylic acid buffering agent or titanium residue removal enhancer. None of the four disclosures cited above discloses the advantages of adding a titanium residue removal enhancer. The present invention has shown that in some cases it is necessary to add a titanium residue removal enhancer for effective cleaning of some residues containing titanium found after a plasma etch process. U.S. Pat. No. 5,759,973 and EP 828,197 disclose the use of a chelating agent selected from sugars such as glucose, fructose or sucrose and sugar alcohols such as xylitol, mannitol and sorbitol. Lab tests of formulations of the present invention with fructose or sorbitol added resulted in a solution that was not as pH stable as formulations having an aminocarboxylic acid or no added chelating or buffering agent added.
Patent application WO 9523999 discloses using tetramethylammonium silicate and ammonium silicate as corrosion inhibitors in solutions used for removing resist from circuit boards. However, the lack of any (ethylenedinitrilo) tetraacetic acid (EDTA) content was described as an advantage of the disclosed formulation. In the present invention, in contrast, the optional use of chelating agents such as EDTA was beneficial.
Other uses of silicate inhibitors include magnetic head cleaners (JP 09,245,311), laundry detergents (WO 9,100,330), metal processing solutions (DE 2,234,842. U.S. Pat. Nos. 3,639,185, 3,773,670, 4,351,883, 4,341,878, EP 743,357, U.S. Pat. No. 4,710,232), rosin flux removers (U.S. Pat. No. 5,549,761), and photoresists (JP 50,101,103).
Both metal ion-free silicates such as tetramethylammonium silicate and metal silicates have been used as components of photoresist developers (U.S. Pat. No. 4,628,023, JP 63,147,163, U.S. Pat. Nos. 4,822,722, 4,931,380, RD 318,056, RD 347,073, EP 62,733). Photoresist developers are used before the etching and oxygen plasma ashing processes to remove patterned photoresist areas which have been altered by exposure to light. This leaves a photoresist pattern on the wafer surface which is typically xe2x80x9chardenedxe2x80x9d by exposure to light and heat to form an etching mask. This mask is used during the plasma etching step and usually removed after this use by an oxygen plasma xe2x80x9cashingxe2x80x9d step. The present invention relates to the removal of residues formed during these last two steps and is unrelated to the photoresist development step addressed by the patents cited in this paragraph.
Solutions prepared by dissolving silicic acid or solid silicon in tetramethylammonium hydroxide (TMAH) have been reported as useful for the passivation of aluminum structures during micromachining (xe2x80x9cAluminum passivation in Saturated TMAHW Solutions for IC-Compatible Microstructures and Device Isolationxe2x80x9d, Sarrow. et al., SPIE Vol. 2879, Proceedings-Micromachining and Microfabrication Process Technology II, The International Society for Optical Engineering, Oct. 14-15, 1996, pp. 242-250). Micromachining applications are outside of the scope of the present invention. The solutions in the cited reference contain about 25 weight percent silicate (expressed as SiO2). This concentration is significantly greater than the concentrations used in the examples of this invention, which range from about 0.01 to about 2.9 weight percent silicate (expressed as SiO2). The use of the chelating agent catechol as a silicon etch rate enhancer is also suggested. In the present invention, increasing the etch rate of silicon would be undesirable since this might damage the silicon dioxide dielectric layers commonly used in integrated circuits as well as the exposed silicon backside of the wafer.
The use of a quaternary ammonium hydroxide in photoresist strippers is disclosed in U.S. Pat. Nos. 4,776,892, 5,563,119; JP 09319098 A2; EP 578507 A2: WO 9117484 A1 and U.S. Pat. No. 4,744,834. The use of chelating and complexing agents to sequester metals in various cleaners has also been reported in WO 9705228, U.S. Pat. Nos. 5,466,389, 5,498,293, EP 812011, U.S. Pat. No. 5,561,105, JP 06216098, JP 0641773, JP 06250400 and GB 1,573,206.
U.S. Pat. No. 5,466,389 discloses an aqueous alkaline containing cleaning solution for microelectronics substrates that contains a quaternary ammonium hydroxide and optional metal chelating agents and is useful for a pH range of about 8 to 10. In the present invention, a pH greater than 10 is required to effect the desired residue removal. In addition, silicates have limited water solubility at about pH 10. Lab tests indicated that when the pH of a tetramethylammonium silicate solution is reduced to about 10 the solution becomes xe2x80x9ccloudyxe2x80x9d as silicates precipitate out of solution.
U.S. Pat. No 5,498,293 discloses a process for using an aqueous alkaline cleaning solution that contains a quaternary ammonium hydroxide and optional metal chelating agents useful for cleaning silicon wafers. The disclosure of this cleaning process is for treatments to substrates before the presence of integrated metal circuits and is used to generate a wafer surface that is essentially silicon dioxide free and would be employed before the use of photoresist for integrated circuit fabrication. The present invention, in contrast, focuses on the cleaning of wafers with integrated circuits present which have been photoresist coated, etched, and oxygen plasma ashed.
None of the compositions disclosed in the prior art effectively remove all organic contamination and metal-containing residues remaining after a typical etching process. There is, therefore, a need for stripping compositions that clean semiconductor wafer substrates by removing metallic and organic contamination from such substrates without damaging the integrated circuits. Such compositions must not corrode the metal features that partially comprise the integrated circuit and should avoid the expense and adverse consequences caused by intermediate rinses.
It is, therefore, an object of the present invention to provide compositions useful in the microelectronics industry for cleaning semiconductor wafer substrates.
It is another object of the present invention to provide compositions that remove metallic and organic contamination from semiconductor wafer substrates without damaging the integrated circuits.
It is another object of the present invention to provide compositions that avoid the expense and adverse consequences caused by intermediate rinses.
It is a further object of the present invention to provide a method for cleaning semiconductor wafer substrates that removes metallic and organic contamination from such substrates without damaging the integrated circuits and avoids the expense and adverse consequences caused by intermediate rinses.
These and other objects are achieved using new aqueous compositions for stripping or cleaning semiconductor wafer substrates that contain one or more metal ion-free bases and a water-soluble metal ion-free silicate. The compositions are placed in contact with a semiconductor wafer substrate for a time and at a temperature sufficient to clean unwanted contaminants and/or residues from the substrate surface.
Preferably, the compositions contain one or more metal ion-free bases dissolved in water in sufficient amounts to produce a pH of about 11 or greater and about 0.01% to about 2% by weight (calculated as SiO2) of a water-soluble metal ion-free silicate. Any suitable base may be used in the compositions of this invention. Preferably, the base is selected from hydroxides and organic amines, most preferably quaternary ammonium hydroxides and ammonium hydroxides.
Any suitable silicate may be used in the compositions of this invention. Preferably, the silicate is selected from quaternary ammonium silicates, most preferably tetramethyl ammonium silicate.
The compositions of the present invention may contain other components such as chelating agents, organic co-solvents, titanium residue removal enhancing agents, and surfactants. Chelating agents are preferably present in amounts up to about 2% by weight, organic co-solvents are preferably present in amounts up to about 20% by weight, titanium residue removal enhancers are preferably present in amounts up to about 30% by weight, and surfactants are preferably present in amounts up to about 0.5% by weight.
The compositions can be used to clean substrates containing integrated circuits or can be used to clean substrates that do not contain integrated circuits. When integrated circuits are present, the composition removes the contaminants without damaging the integrated circuits.
The method for cleaning semiconductor wafer substrates of the present invention requires that the compositions of the present invention be placed in contact with a semiconductor wafer substrate for a time and at a temperature sufficient to clean unwanted contaminants and/or residues from the substrate surface. The method includes both bath and spray applications. Typically, the substrate is exposed to the composition for the appropriate time and at the appropriate temperature, rinsed using high purity de-ionized water, and dried.
The compositions clean wafer substrates by removing metallic and organic contamination. Importantly, the cleaning process does not damage integrated circuits on the wafer substrates and avoid the expense and adverse consequences associated by intermediate rinses required in prior methods.
Other objects, advantages, and novel features of the present invention will become apparent in the following detailed description of the invention.
The present invention provides new aqueous compositions for stripping or cleaning semiconductor wafer substrates that contain one or more metal ion-free bases and a water-soluble metal ion-free silicate. Preferably, the invention provides aqueous, alkaline stripping or cleaning compositions comprising one or more alkaline metal ion-free base components in an amount sufficient to produce a solution pH of about 11 or greater, preferable from about pH 11 to about pH 13, and a metal ion-free water-soluble silicate concentration by weight (as SiO2) of about 0.01% to about 5%, preferably from about 0.01% to about 2%.
The compositions may also contain a chelating agent in a concentration by weight of about 0.01% to about 10%, generally from about 0.01% to about 2%. Further optional components are water-soluble organic solvents in a concentration by weight of about 0. 1% to about 80%, generally about 1% to about 30%, titanium residue removal enhancers in a concentration by weight of about 1% to about 50%, generally about 1% to about 30%, and a water-soluble surfactant in an amount by weight of about 0.01% to about 1%, preferable about 0.01% to about 0.5%.
The composition is an aqueous solution containing the base, the silicate, the optional components, if any, and water, preferably high purity de-ionized water.
Any suitable base may be used in the compositions of the present invention. The bases are preferably quaternary ammonium hydroxides, such as tetraalkyl ammonium hydroxides (including hydroxy- and alkoxy-containing alkyl groups generally of from 1 to 4 carbon atoms in the alkyl or alkoxy group). The most preferable of these alkaline materials are tetramethyl ammonium hydroxide and trimethyl-2-hydroxyethyl ammonium hydroxide (choline). Examples of other usable quaternary ammonium hydroxides include: trimethyl-3-hydroxypropyl ammonium hydroxide, trimethyl-3-hydroxybutyl ammonium hydroxide, trimethyl-4-hydroxybutyl ammonium hydroxide, triethyl-2-hydroxyethyl ammonium hydroxide, tripropyl-2-hydroxyethyl ammonium hydroxide, tributyl-2-hydroxyethyl ammonium hydroxide, dimethylethyl-2-hydroxyethyl ammonium hydroxide, dimethyldi(2-hydroxyethyl) ammonium hydroxide, monomethyltri(2-hydroxyethyl) ammonium hydroxide, tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, tetrabutyl ammonium hydroxide, monomethyl-triethyl ammonium hydroxide, monomethyltripropyl ammonium hydroxide, monomethyltributyl ammonium hydroxide, monoethyltrimethyl ammonium hydroxide, monoethyltributyl ammonium hydroxide, dimethyldiethyl ammonium hydroxide, dimethyldibutyl ammonium hydroxide, and the like and mixtures thereof.
Other bases that will function in the present invention include ammonium hydroxide, organic amines particularly alkanolamines such as 2-aminoethanol, 1-amino-2-propanol, 1-amino-3-propanol, 2-(2-aminoethoxy)ethanol, 2-(2-aminoethylamino)ethanol, 2-(2-aminoethylamino)ethylamine and the like, and other strong organic bases such as guanidine, 1,3-pentanediamine, 4-aminomethyl-1,8-octanediamine, aminoethylpiperazine, 4-(3-aminopropyl)morpholine, 1,2-diaminocyclohexane, tris(2-aminoethyl)amine, 2-methyl-1,5-pentanediamine and hydroxylamine. Alkaline solutions containing metal ions such as sodium or potassium may also be operative, but are not preferred because of the possible residual metal contamination that could occur. Mixtures of these additional alkaline components, particularly ammonium hydroxide, with the aforementioned tetraalkyl ammonium hydroxides are also useful.
Any suitable metal ion-free silicate may be used in the compositions of the present invention. The silicates are preferably quaternary ammonium silicates, such as tetraalkyl ammonium silicate (including hydroxy- and alkoxy-containing alkyl groups generally of from 1 to 4 carbon atoms in the alkyl or alkoxy group). The most preferable metal ion-free silicate component is tetramethyl ammonium silicate. Other suitable metal ion-free silicate sources for this invention may be generated in-situ by dissolving any one or more of the following materials in the highly alkaline cleaner. Suitable metal ion-free materials useful for generating silicates in the cleaner are solid silicon wafers, silicic acid, colloidal silica, fumed silica or any other suitable form of silicon or silica. Metal silicates such as sodium metasilicate may be used but are not recommended due to the detrimental effects of metallic contamination on integrated circuits.
The compositions of the present invention may also be formulated with suitable metal chelating agents to increase the capacity of the formulation to retain metals in solution and to enhance the dissolution of metallic residues on the wafer substrate. Typical examples of chelating agents useful for this purpose are the following organic acids and their isomers and salts: (ethylenedinitrilo)tetraacetic acid (EDTA), butylenediaminetetraacetic acid, cyclohexane-1,2-diaminetetraacetic acid (CyDTA), diethylenetriaminepentaacetic acid (DETPA), ethylenediaminetetrapropionic acid, (hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), N,N,Nxe2x80x2,Nxe2x80x2-ethylenediaminetetra(methylenephosphonic) acid (EDTMP), triethylenetetraminehexaacetic acid (TTHA), 1,3-diamino-2-hydroxypropane-N,N,Nxe2x80x2,Nxe2x80x2-tetraacetic acid (DHPTA), methyliminodiacetic acid, propylenediaminetetraacetic acid, nitrolotriacetic acid (NTA), citric acid, tartaric acid, gluconic acid, saccharic acid, glyceric acid, oxalic acid, phthalic acid, maleic acid, mandelic acid, malonic acid,lactic acid, salicylic acid, catechol, gallic acid, propyl gallate, pyrogallol, 8-hydroxyquinoline, and cysteine.
Preferred chelating agents are aminocarboxylic acids such as EDTA. Chelating agents of this class have a high affinity for the aluminum-containing residues typically found on metal lines and vias after plasma xe2x80x9cashingxe2x80x9d. In addition, the pKa""s for this class of chelating agents typically include one pKa of approximately 12 which improves the performance of the compositions of the invention.
The compositions of the present invention may also contain one or more suitable water-soluble organic solvents. Among the various organic solvents suitable are alcohols, polyhydroxy alcohols. glycols, glycol ethers, alkyl-pyrrolidinones such as N-methylpyrrolidinone (NMP), 1-hydroxyalkyl-2-pyrrolidinones such as 1-(2-hydroxyethyl)-2-pyrrolidinone (HEP), dimethylformamide (DMF), dimethylacetamide (DMAc), sulfolane or dimethylsulfoxide (DMSO). These solvents may be added to reduce aluminum and/or aluminum-copper alloy and/or copper corrosion rates if further aluminum and/or aluminum-copper alloy and/or copper corrosion inhibition is desired. Preferred water-soluble organic solvents are polyhydroxy alcohols such as glycerol and/or 1-hydroxyalkyl-2-pyrrolidinones such as 1-(2-hydroxyethyl)-2-pyrrolidinone (HEP).
The compositions of the present invention may also contain one or more suitable titanium residue removal enhancers. Among the various titanium residue removal enhancers that are suitable are hydroxylamine, hydroxylamine salts, peroxides, ozone and fluoride. Preferred titanium residue removal enhancers are hydroxylamine and hydrogen peroxide.
The compositions of the present invention may also contain any suitable water-soluble amphoteric, non-ionic, cationic or anionic surfactant. The addition of a surfactant will reduce the surface tension of the formulation and improve the wetting of the surface to be cleaned and therefore improve the cleaning action of the composition. The surfactant may also be added to reduce aluminum corrosion rates if further aluminum corrosion inhibition is desired.
Amphoteric surfactants useful in the compositions of the present invention include betaines and sulfobetaines such as alkyl betaines, amidoalkyl betaines, alkyl sulfobetaines and amidoalkyl sulfobetaines; aminocarboxylic acid derivatives such as amphoglycinates, amphopropionates, amphodiglycinates, and amphodipropionates; iminodiacids such as alkoxyalkyl iminodiacids or alkoxyalkyl iminodiacids; amine oxides such as alkyl amine oxides and alkylamido alkylamine oxides; fluoroalkyl sulfonates and fluorinated alkyl amphoterics; and mixtures thereof.
Preferably, the amphoteric surfactants are cocoamidopropyl betaine, cocoamidopropyl dimethyl betaine, cocoamidopropyl hydroxy sultaine, capryloamphodipropionate, cocoamidodipropionate, cocoamphopropionate, cocoamphohydroxyethyl propionate, isodecyloxypropylimino dipropionic acid, laurylimino dipropionate, cocoamidopropylamine oxide and cocoamine oxide and fluorinated alkyl amphoterics.
Non-ionic surfactants useful in the compositions of the present invention include acetylenic diols, ethoxylated acetylenic diols, fluorinated alkyl alkoxylates, fluorinated alkylesters, fluorinated polyoxyethylene alkanols, aliphatic acid esters of polyhydric alcohols, polyoxyethylene monoalkyl ethers, polyoxyethylene diols, siloxane type surfactants, and alkylene glycol monoalkyl ethers. Preferably, the non-ionic surfactants are acetylenic diols or ethoxylated acetylenic diols.
Anionic surfactants useful in the compositions of the present invention include carboxylates, N-acylsarcosinates, sulfonates, sulfates, and mono and diesters of orthophosphoric acid such as decyl phosphate. Preferably, the anionic surfactants are metal-free surfactants.
Cationic surfactants useful in the compositions of the present invention include amine ethoxylates, dialkyldimethylammonium salts, dialkylmorpholinum salts, alkylbenzyldimethylammonium salts, alkyltrimethylammonium salts, and alkylpyridinium salts. Preferably, the cationic surfactants are halogen-free surfactants.
In the preferred embodiment of the present invention, the composition is an aqueous solution containing about 0.1-2% by weight tetramethylammonium hydroxide (TMAH) and about 0.01-1% by weight (calculated as % SiO2,) tetramethylammonium silicate (TMAS).
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-2% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA), and about 0.01-1% by by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS).
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-2% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA),about 0.01-1% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS), and about 0.5-20% by weight of polyhydroxy compounds, preferably glycerol.
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-2% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA), about 0.01-1% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS), about 0.5-20% by weight of polyhydroxy compounds, and about 0.01-0.3% by weight of a nonionic ethoxylated acetylenic diol surfactant.
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-2% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraactic acid (CyDTA),about 0.01-1% by weight (calculated as % SiO2)tetramethylammonium silicate (TMAS), and about 0.5-20% by weight of an alkyl-pyrrolidinone such as 1-(2-hydroxyethyl)-2-pyrrolidinone (HEP), preferably 1-(2-hydroxyethyl)-2-pyrrolidinone (HEP).
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-2% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA), about 0.01-1% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS), about 0.5-20% by weight of an alkyl-pyrrolidinone such as 1-(2-hydroxyethyl)-2-pyrrolidinone (HEP), and about 0.01-0.3% by weight of a nonionic ethoxylated acetylenic diol surfactant.
In a preferred embodiment of the present invention, the composition is an aqueous solution containing about 0.1-10% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS) and about 1-10% by weight hydrogen peroxide.
In another preferred embodiment of the present invention, the composition is an aqueous solution containing about 0.1-9% by weight tetramethylammonium hydroxide (TMAH), about 0.01-4% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS) and about 1-20% by weight hydroxylamine.
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-10% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA),about 0.01-1% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS) and about 1-10% by weight hydrogen peroxide.
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-9% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA), about 0.01-4% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS) and about 1-20% by weight hydroxylamine.
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-10% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA), about 0.01-1% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS), about 1-10% by weight hydrogen peroxide, and about 0.01-0.3% by weight of a nonionic ethoxylated acetylenic diol surfactant.
In another embodiment of the present invention, the composition is an aqueous solution containing about 0.1-9% by weight tetramethylammonium hydroxide (TMAH), about 0.01-1% by weight trans-(1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA), about 0.01-4% by weight (calculated as % SiO2) tetramethylammonium silicate (TMAS), about 1-20% by weight hydroxylamine, and about 0.01-0.3% by weight of a nonionic ethoxylated acetylenic diol surfactant.
In all the embodiments, the balance of the composition is made up with water, preferably high purity de-ionized water.
As shown in the examples below, compositions containing only the alkaline base are unable to produce effective cleaning action without corroding the aluminum metal integrated circuit features. The examples also show the utility of adding a soluble silicate to the highly basic formulations to (1) protect the aluminum metal integrated circuits from corrosion, (2) extend the solution bath life of these cleaner compositions by silicate buffering (pKa2=11.8), and (3) decrease the silicon dioxide dielectric etch rate. Additional advantages of the compositions of the present invention are: (1) high water content that facilitates immediate rinsing with water without an intermediate (such as isopropanol) rinse to prevent post-cleaning metal corrosion and that results in negligible carbon contamination of the substrate surface, (2) reduced health, safety, environmental, and handling risks associated with the use of non-toxic components specifically avoiding catechol, volatile organic solvents, and organic amines characteristic of prior art compositions used to strip and clean integrated circuit substrates, (3) ability to remove titanium containing residues from integrated circuit substrates at low temperatures, (4) compatibility of these formulations with sensitive low k dielectric materials used in integrated circuits, (5) compatibility (low etch rates) with copper, and (6) ability of the compositions of this invention to clean and prevent contamination of a wafer substrate during a post chemical mechanical polishing (CMP) operation.
The method of the present invention cleans semiconductor wafer substrates by exposing the contaminated substrate to the compositions of the present invention for a time and at a temperature sufficient to clean unwanted contaminants from the substrate surface. Optionally, the substrate is rinsed to remove the composition and the contaminants and dried to remove any excess solvents or rinsing agents. The substrate can then be used for its intended purpose.
Preferably, the method uses a bath or spray application to expose the substrate to the composition. Bath or spray cleaning times are generally 1 minute to 30 minutes, preferably 5 minutes to 20 minutes. Bath or spray cleaning temperatures are generally 10xc2x0 C. to 85xc2x0 C., preferably 20xc2x0 C. to 45xc2x0 C.
If required, the rinse times are generally 10 seconds to 5 minutes at room temperature, preferably 30 seconds to 2 minutes at room temperature. Preferably de-ionized water is used to rinse the substrates.
If required, drying the substrate can be accomplished using any combination of air-evaporation, heat, spinning, or pressurized gas. The preferred drying technique is spinning under a filtered inert gas flow, such as nitrogen, for a period of time until the wafer substrate is dry.
The method of the present invention is very effective for cleaning semiconductor wafer substrates that have been previously oxygen plasma ashed to remove bulk photoresist, particularly wafer substrates containing a silicon, silicon oxide, silicon nitride, tungsten, tungsten alloy, titanium, titanium alloy, tantalum, tantalum alloy, copper, copper alloy, aluminum or aluminum alloy film. The method removes unwanted metallic and organic contaminants but does not cause unacceptable corrosion to the silicon, silicon oxide, silicon nitride, tungsten, tungsten alloy, titanium, titanium alloy, tantalum, tantalum alloy, copper, copper alloy, aluminum or aluminum alloy film.